This invention relates to a fire-screening glazing panel comprising a first structural ply formed by a vitreous sheet and at least a second structural ply.
The expression "vitreous material" as used herein comprises glass and vitrocrystalline material. Vitrocrystalline material is formed by subjecting a glass to a thermal treatment so as to induce the formation of one or more crystalline phrases therein.
In the construction of buildings, glazing panels have often to be used in exterior or interior walls or partitions. An obvious example is the use of transparent glazing panels to form windows. Opaque glazing panels are also used, e.g. to form partitions.
Such panels often must satisfy standards of fire resistance, which standards require the panel on the outbreak of fire to have a minimum strength retention time, to be completely flame-proof, and to satisfy certain stringent tests of thermal insulating power to ensure that the panel will prevent propagation of fire by heat radiation from the panel and will not become so hot as to involve risk of seriously burning a person who may touch the panel while it is exposed to fire.
The standard of fire resistance of a given panel can be quantified as a function of the time for which that panel satisfies one or more of the above criteria during a test in which the panel is exposed to the interior of an enclosure whose temperature is raised according to a predetermined schedule.
Ordinary glass panes are not highly thermally insulating or fire resistant. When exposed to fire they become very hot and consequently cannot be touched without the risk of severe burning. Moreover, heat radiation from the pane can itself constitute a further fire-hazard.
It has accordingly been proposed to incorporate a layer of an intumescent material in a panel, e.g., laminated between two sheets of glass (see U.S. Pat. No. 3,640,837; also see British Pat. No. 933,410). The intumescent material most often used is hydrated sodium silicate. If such a laminate is exposed to fire, the combined water in the hydrated sodium silicate layer is driven off, and the layer foams and the material is converted into a porous opaque mass which is very effective as a thermal barrier. Also during such heat-conversion of the layer, its temperature remains substantially constant so that excessive heating of the glass sheet remote from the fire is delayed.
It has been found however, that layers of intumescent material incorporated in light-transmitting panels tend to degrade with age when exposed to the sun or another heat source and that this results in reduced effectiveness on heat-conversion when the panel is exposed to fire, and for transparent panels, results in a loss of overall transparency.
It is an object of the present invention to provide means affording an increase in resistance to aging in fire-screening glazing panels and/or in the degree of fire-resistance.
Accordingly, the present invention, as broadly defined resides in a fire-screening glazing panel comprising a first structural ply formed by a vitreous sheet and at least a second structural ply characterised in that there is provided between said plies at least one layer of intumescent material and such panel includes at least one ply which bears at least one infra-red reflecting coating isolated from said intumescent material.
The intumescent material is isolated from the infra-red reflecting coating material so as to avoid any possibility of reaction between them.
The advantage afforded by the present invention over a correspondingly dimensioned panel which lacks an infra-red reflecting coating will depend, inter alia, on the reflection spectrum of the coating and, when only one coating is present, on the location of the coating with respect to the intumescent layer.
The most important advantages are at present believed to be afforded when the coated ply or plies reflect(s) substantial proportions of incident infra-red radiation having short wavelengths e.g., 0.7 to 3 .mu.m, and the panel is oriented so that the (or one of the) coated ply is situated so as to protect the intumescent material from solar radiation. The greater part of the infra-red energy radiated by the sun lies in this wavelength range, and it is believed to be this energy which is in larger part to cause of aging of fire-screening panels of the type in view. Accordingly, screening the intumescent material with an infra-red reflecting layer reduces the rate at which a panel degrades with age. The problem of aging of fire-screening panels has been identified, the source of the problem has been identified, and the solution to the problem found.
Another advantage is apparent in the case where the coated ply or plies reflect(s) substantial proportions of radiation having longer wavelengths only, while transmitting substantial proportions of short wavelength infra-red radiation. This is because the greater part of the infra-red energy radiated by a fire has such longer wavelengths. If the or a coated ply is between a fire and the intumescent material, then that material will take longer to heat to a given temperature and will thus provide a more effective thermal barrier. The panel will also age less quickly.
It is often found that infra-red reflecting coatings which act to reflect substantial proportions of short wavelength infra-red radiation have the additional advantage of being effective at longer wavelengths as well.
The panel may include two said coated plies with the or each said layer of intumescent material located between them, so that the requirement to orient the panel in a particular way may be obviated.
Preferably at least one said layer of intumescent material is sandwiched between said first and second structural plies and at least one structural ply of said sandwich bears an infra-red reflecting coating on a face which forms an exterior face of the sandwich since this avoids any risk of degradation of the coating due to its possible reaction with the intumescent material.
Preferably the panel comprises at least one other structural ply in addition to the first and second structural plies. Such an additional ply may for example, be laid up against a reflection-coated face of a said sandwich, and may be bonded thereto. This has the advantage of minimizing the risk of damage to such coating by abrasion or weathering.
In preferred embodiments, the additional structural ply or plies define(s) with said first and/or second structural ply at least one inter-ply space, and at least one ply face which forms a boundary of such a space bears an infra-red reflecting coating. This has the advantage of substantially avoiding any damage to such a coating. In such cases, it is preferred that an infra-red reflecting coating is carried by a face of the or at least one said additional ply, since this is found most convenient. Such a double panel also affords improved thermal insulation.
Preferably there is at least one infra-red reflecting coating which comprises a metal selected from the group consisting of aluminium, copper, gold, silver, palladium. Such metals can form thin coatings which are transparent to visible light and are highly reflective of infra-red radiation. For example, a coating of gold 250 A thick can afford a visible light transmission of about 30% while reflecting 90% of infra-red radiation having a wavelength equal to 2.5 .mu.m.
The thickness of a metallic infra-red reflecting coating may be chosen as a function of the desired infra-red reflection and visible light transmission. Thus, for example, a gold coating might have a thickness between 100 A and 400 A. In order to give good infra-red reflection, the coating should not normally be thinner, and thicker coatings will not transmit sufficient visible light for use with transparent panels. It should be noted that metallic coatings are effective over a very wide range of wavelengths and thus can screen a panel against infra-red radiation from the sun or from a fire.
A metal coating may be combined with one or more oxide coatings deposited above or below the metal coatings to provide an infra-red filter, as is known. An oxide coating may also be used alone or in combination with other oxides or metallic compounds to form interference filters, as is also well known. Thus, alternatively, or in addition, it is advantageous to provide at least one infra-red reflecting coating which comprises a metal oxide. Such oxides are for example, oxides from silicon, titanium, zirconium, aluminium, tantalum. Other metallic compounds which may be used for the infra-red reflecting coating are for example, sulfides, nitrides and carbides, and other coatings are also suitable.
Advantageously a metal oxide is selected from the group of far-infrared reflecting oxides. For example, an indium oxide coating can give good results especially as regards this range of infra-red radiation having longer wavelengths, say 3 .mu.m and above. Other oxides, e.g. tin oxide may also be used for this purpose. Such a metal oxide coating may contain a doping agent for example ions of chlorine, fluorine, arsenic or antimony, as is well known. The thickness of such oxide coatings is preferably between 1000 A and 6000 A.
The intumescent material may comprise a hydrated metal salt. Examples of metal salts which can be used in hydrated form are as follows: aluminates, plumbates, stannates and alums, e.g. of sodium or potassium; borates, e.g. sodium borate, and phosphates, e.g., orthophosphates of sodium or potassium and aluminium phosphate.
Hydrated alkali metal silicates, e.g., sodium silicate, are also suitable for use in a layer incorporating intumescent material.
Such substances have very suitable properties for use in fire-screening panels. They are in many cases capable of forming transparent layers which adhere well to glass or vitrocrystalline material. On being sufficiently heated, the combined water boils and the layers foams, so that the hydrated metal salt is converted into an opaque solid, porous or cellular form in which it is highly thermally insulating and remains adherent to the glass or vitrocrystalline material.
This feature is particularly important, since even if all the structural plies of the panel are cracked or broken by thermal shock, the panel may retain its effectiveness as a barrier against heat and fumes since the fragments of the plies may remain in position bonded together by the converted metal salt.
In some embodiments, a layer of intumescent material is used which is merely translucent, but preferably the material forms a transparent solid layer at ambient temperature.
The use of hydrated sodium silicate is especially preferred since it can readily be formed into solid transparent layers.
Preferably, first and second structural plies and at least one layer of intumescent material form a laminate whose various plies are bonded together in face-to-face relation.
Advantageously, between said first and second structural plies there is located at least one plastics membrane and, on opposite sides of such membrane(s), layers of intumescent material. This feature has a particular advantage as regards fire resistance. If a panel incorporating such a laminate is exposed to fire, the layer which is nearer the fire intumesces. As this layer is heated, the other intumescent layer is kept at a somewhat lower temperature until conversion of the first layer is completed. This prolongs the time taken for the structural ply further from the fire to become heated to a given temperature, and also reduces any tendency for that ply to become nonuniformly heated. This in turn reduces the possibility that that ply will be broken as a result of thermal shock.
Preferably, at least one said layer intumescent material is between 0.1 mm and 8 mm in thickness. Layers having this range of thickness can be converted to become very effective fire-screening barriers. It is clear that the effectiveness of a fire-screening barrier formed from a layer of given material will depend on its thickness, but also, the transparency of such a layer will be less with increased thickness.
Preferably, a panel according to the invention is transparent, and preferably also, each structural ply comprises a vitreous sheet.
Advantageously, at least one structural ply comprises a tempered vitreous sheet. A tempered vitreous sheet is able to withstand considerable thermal shocks. Chemically tempered sheets are particularly recommended.